Apparatus for vacuum coating electrical resistors



Dec. 17, 1957 s'. A. JOHNSON ,8

APPARATUS FOR VACI JUM COATING ELECTRICAL RESISTORS 7 Filed April 9,1954 2 Sheets-Sheet 1 1N VENTOR I STANLEY A. JOHN SON ATTORNEY Dec. 17',1957 s. A. JOHNSON ,81

APPARATUS FOR VACUUM COATING ELECTRICAL RESISTORS Filed April 9, 1954 2Sheets-Sheet 2 INVENT OR ATTORNEY United States Patent APPARATUS FORVACUUM COATING ELECTRICAL RESISTORS Stanley A. Johnson, Brooklyn, N. Y.,assignor to Polytechnic Research & Development C0,, lnc., Brooklyn, N.Y., a corporation of New York Application April 9, 1954, Serial No.422,169

6 Claims. (Cl. 118-8) This invention relates to apparatus for producingelectrical resistors of the type comprising metallic films depositedupon tubular or cylindrical dielectric carriers. While my invention isespecially useful for the production of electrical resistors, it is notlimited to such use and may have other uses in the coating art.

One object of the invention is to devise apparatus for coating carriersin which the carriers are automatically loaded upon a moving carriagefrom a bulk supply and are conveyed by the carriage through a coatingzone where the coating is applied to the carriers.

Another object of the invention is to devise an arrangement in which thefilm deposited upon the tubular carrier is of uniform thickness aroundthe entire cylindrical surface of the carrier. Provision is made torotate each carrier about its own axis as it passes through the coatingzone.

A further object of the invention is to devise apparatus for applyingcoatings to a plurality of tubular carriers in such a manner that thecoatings on all of the carriers will be uniform. This is accomplished byautomatically controlling the speed of conveying the carriers throughthe coating zone in response to a device which senses or measures acharacteristic of the coating on the carriers as they leave the coatingzone.

Another object of the invention is to devise apparatus for applying aprotective film over a thermally evaporated metallic film beforeexposing the metallic film to the atmosphere. Both coating operationsare carried on at the same time but in different sections of the coatingzone.

A preferred form of the invention is illustrated in the accompanyingdrawing, in which:

Figure 1 is a side elevational view of the apparatus with one of theside supporting members removed;

Figure 2 is a sectional View on an enlarged scale taken along the line2-2 of Figure 1;

Figure 3 is an enlarged fragmentary view showing details of theconstruction in the same area as that of Figure 2; and

Figure 4 is an end elevational view of the apparatus including aschematic representation of the means for controlling the operation ofthe apparatus.

Referring to Figure 1 of the drawing, the apparatus is mounted on a baseplate 1 and enclosed by a bell jar 2. The enclosure thus formed isevacuated by means of suitable apparatus not forming a part of thisinvention and not shown. Two side members 3 are held in spaced relationby spacers 4 and form the main supporting structure of the apparatus.Mounted on the uppermost portion of the supporting structure is ahousing 5 containing heating coil 6 and enclosing a removable hopper 7which contains a supply of carriers to be coated. In this instance thecarriers are formed of short sections C of glass tubing which have beenfire polished on each end and have had a conducting collar Ca formed oneach end by any well known process, see Figure 2. Immediately below thehousing 5 is the feed wheel 3 for transferring carriers from hopper 7 toa movable carriage. This wheel has radial slots 8a formed in itsperiphery for the purpose of receiving carriers from hopper 7. TransferWheel 8 is located immediately below the hopper 7, the bottom of thehopper being open and the sides of the hopper conforming with theperiphery of the Wheel 8 so that carriers contained within the hoppermay fall by gravity into the slots 8a. A curved guide 23 is provided tohold the carriers in the radial slots 8a of feed wheel 8 while they arebeing transferred to a movable carriage comprising carrier wheel 9. Thehopper '1 may be removed through the open top of the housing 5 by thefinger tab 7a. When the hopper is filled with carriers, the bottom isclosed by a curved, sliding wall section which may be removed through anopening in one of the side members 3 after the hopper is in positionabove the wheel 8.

In order to provide an unobstructed coating zone and convenient accessto the coating material sources, carrier wheel 9 is constructed of twoannular rings supported in spaced relation by grooved rollers 22 whichare mounted on side members 3. The peripheries of these rings haveradial slots 9a formed therein for the purpose of receiving the tubularcarriers, and the pitch or spacing between the cen ers of the radialslots in the carrier wheel 9 and in the feed wheel 8 are identical. Inorder to rotate the carrier Wheel 9 and maintain the two rings in properrelationship or alignment, a driving wheel 19 is provided having mountedthereon a series of rollers 21 which are of approximately the samediameter as the tubular carriers. The pitch or spacing between thecenter lines of the rollers 21 is identical with the pitch of the radialslots in carrier wheel 9 and feed wheel 8. As the feed wheel 19 rotatesin a counterclockwise direction, the rollers 21 successively engagecorresponding radial slots 9a in the carrier Wheel 9, thereby causingcarrier wheel 9 to rotate in a clockwise direction. Suitable gearing isprovided between driving wheel 19 and feed wheel 8 so as to maintaincarrier wheel 9 and feed wheel 8 in synchronisrn at all times. 2

Referring now to Figures 2 and 3 of the drawing, it will be seen thatside members 3 have formed on the inside faces thereof arcuatestationary tracks 10. These tracks are shown as forming a completecircle on each side member, but, if so desired, the lower portions ofthe track may be omitted. These tracks are provided to support the endsof the tubular carriers and are so positioned that the carriers do nottouch the bottom of radial slots 9a in the carrier wheel 9. As thetubular carriers are transferred to the radial slots 9a of the carrierwheel 9, they rest upon the stationary tracks 10 and the rotation of thecarrier wheel 9 causes them to roll along the tracks, thereby effectingrotation of each carrier about its own axis. In order to assure thecontinued uniform rotation of the tubular carriers, it has been founddesirable to vibrate the sections of track 10 which extend over thecoating zone in such a manner as will tend to cause the car riers torotate independently of the rotation caused by the carrier wheel 9. Thisis accomplished by isolating a section 3a of each side member 3 andproviding suiticient clearance around it to allow the desired vibrationto take place. These isolated sections 3a are supported by means ofsprings 25 which have one end fixed to the side members 3 and the otherend attached to posts 27 mounted on sections 3a. The angular position ofthese springs will determine the direction in which sections 3a arepermitted to vibrate and the vibration is set up by the rotation oftoothed wheel 26 which engages one of the posts 27. As shown in Figure3, the mounting springs 25 are arranged with their axes at an angle tothe adjacent track 19 so that the isolated track sections are vibratedwith a component of movement parallel with the track and anothercomponent transversely of the track. The arrangement is such that whenthe isolated track sections are being moved upwardly, theysimultaneously move rearwardly in opposition to the direction ofrotation of the carrier wheel 9. While this is the preferredarrangement, some advantage may be obtained by vibrating the isolatedtrack sections in a vertical direction only.

Returning now to Figure 1, it will be seen that the coating zone isdivided into a first section and a second section by a baffle 13.Mounted within the inner circumference of carrier wheel 9 so as toirradiate the first portion of the coating zone is a source 11 of amolecular radiation of a suitable metal to form the resistive coating,such as chromium or a nickel-chromium alloy. Similarly mounted on theopposite side of bafile 13 in such a position as to irradiate the secondsection of the coating zone is a source 12 of vaporized protectivecoating material such as silicon monoxide.

At the opposite end of the coating zone from feed wheel 8 is a deliverywheel 15 of similar construction to that of feed wheel 8. An unloadingramp 24 is provided between rings 9 to transfer the carriers fromcarrier wheel 9 to delivery wheel 15. As the carriers are transferred todelivery wheel 15, it is caused to rotate and rotation of wheel 15 movesthe carriers onto two contact blocks 16a and 16b which are insulatedfrom each other and from other parts of the machine. In order to avoidthe possibility of the first carrier to be transferred jamming theapparatus before synchronism is established between delivery wheel 15and carrier wheel 9, delivery wheel 15 1S spring mounted by means notshown. Contact blocks 16a and 161) are positioned to engage the lowresistance collars carried at the ends of the carriers, and these blocksare provided with connection leads which extend through the base 1 forpurposes indicated below. These contact blocks are sufiiciently long sothat by the time one carrier is 1n a position to move ofl? of the rearend of the block, another carrier is in position to move onto the blockat the front end. As the carriers pass beyond the outer end of thecontact blocks, they drop out of the slots in the wheel 15 and areconveyed by any suitable means, such as an inclined chute. to the bottomof the bell jar where they may be deposited either upon the base 1 orwithin a suitable tray or bucket enclosed within the jar.

The feed wheel 8 and the driving Wheel 19 are driven by a suitable powersource, such as the electric motor 18 mounted below the base 1 andhaving a drive shaft 18a extending through the base and driving a geartrain 20 which in turn drives shafts 8b and 19a of wheels 8 and 19. Theoperation of the coating apparatus described above is believed to beobvious from the description. The preferred conditions for producing asatisfactory resistor by the thermal evaporation process carried out bythis apparatus are set forth in U. S. Patent No. 2,586,752.

Since the thickness of the film formed on the tubular carriers isaffected by the speed of rotation of carrier wheel 9. it is desirable togovern this speed of rotation in order to maintain a uniform thicknessof film on all the carriers. For this purpose contact blocks 16a and 16bare connected to a suitable electric circuit for sensing or measuringthe resistance of the metallic film deposited on the carriers by thesource 11, and a suitable control arrangement responds to a change inresistance from a desired value to vary the speed of the carrier wheelin a direction to restore the resistance to the desired value. Onesuitable sensing circuit and control arrangement is showndiagrammatically in Figure 4. The sensing circuit comprises a Wheatstonebridge having two arms and 31 connected in series between diagonalpoints (a) and (b) and another pair of arms formed of resistor 32 andthe resistor element resting on contact blocks 16a and 16b and alsoconnected in series across points (a) and (b). A suitable source ofcurrent 33 is connected across the other pair of diagonal points (0) and(d) and a zerocenter current-responsive device 34 is connected betweendiagonal points (a) and (b). The bridge is adjusted so that when thecoated resistor has a desired resistance value, the bridge is balancedand the armature 35 of the current device 34 is in neutral position. Ifthe resistance value varies from the desired value, the armature 35 willmove in one direction or the other, depending upon whether theresistance value is greater or less than the desired value. Armature 35is arranged to control the direction of rotation of a pilot motor havingan armature 36 and a divided field winding 36a and 36b. The motorarmature is energized from a suitable supply circuit 37, and connectionsare controlled by armature 35 to energize one or the other field windingsections 36a or 36b, to drive the motor armature 36 in one direction orthe other when the armature 35 moves from its neutral position. Themotor 36 operates with suitable means represented by the threaded shaftand collar 38 to vary the resistance 39 which is connected in theenergizing circuit of the field winding 18b of motor 18, the armature ofmotor 18 being constantly energized from supply circuit 37.

The control circuit shown in Figure 4 is arranged so that an increase inresistance of the coated resistors above the desired value will efiect aslowing down of the speed of the motor 18, and a decrease in theresistance value below that desired will effect an increase in the speedof the operation of the motor 18. So long as the coated films are of thedesired resistance value, the armature 35 will remain in neutralposition and the motor 18 will operate at a constant speed. It will beobvious that other arrangements than the particular arrangementillustrated and described may be employed for regulating the speed ofthe carrier wheel 9. Also, other devices may be used to sense thethickness of the coating.

I claim:

1. Film forming apparatus comprising a movably mounted carriage havingmeans thereon to convey a plurality of carriers to be coated through acoating zone, means to rotate said carriers with respect to saidcarriage while traversing said coating zone, means for storing a supplyof said carriers, means for loading said stored carriers on saidcarriage at one end of said coating zone, a vacuum chamber enclosingsaid carriage, said rotating means, said storage means and said loadingmeans, and a source of molecular radiation arranged within said chamberto simultaneously irradiate said carriers as they pass through saidcoating zone.

2. Apparatus for depositing films upon cylindrical carriers comprising,in combination, a movably mounted carriage having means thereon toconvey a plurality of carriers in succession through a coating zone, twotracks mounted adjacent to and parallel with said carriage through saidcoating zone, said carriers being supported at their ends upon saidtracks and being free to roll on said tracks as they are conveyedthrough said coating zone, means to deposit a film on said carriers asthey pass through said coating zone, and means to vibrate said tracks ina plane perpendicular to the axis of said carriers.

3. Film forming apparatus comprising a movably mounted carriage havingmeans thereon to convey a plurality of carriers through a coating zone,means to rotate said carriers with respect to said carriage whiletraversing said coating zone, means for storing a supply of saidcarriers, means for heating said stored c'arriers, means for loadingsaid stored carriers on said carriage in succession at one end of saidcoating zone, a vacuum chamber enclosing said carriage, said rotatingmeans, said storage means, said heating means, and said loading means, asource of metallic molecular radiation arranged within said chamber toirradiate said carriers as they pass through the first section of saidcoating zone, and a source or" non-metallic molecular radiation arrangedwithin said chamber to irradiate said carriers as they pass through theremaining section of said coating zone.

4. Apparatus according to claim 3 wherein said rotating means comprisestwo stationary tracks mounted adjacent to and parallel with saidcarriage to support the ends of said carriers in rolling relation withsaid tracks, and means to vibrate said stationary tracks in a planeperpendicular to the axis of said carriers.

5. Apparatus according to claim 4 and including means mounted withinsaid chamber for sensing the conductivity of the metallic film formed onsaid carriers, and means responsive to variations in said conductivityto vary the speed of said carriage.

6. Apparatus for depositing films upon cylindrical carriers comprising,in combination, a carrier wheel comprising two annular carrier ringsmounted in spaced coaxial relation and having radial slots formed in theperiphery thereof to receive said carriers, two stationary, arcnatetracks mounted adjacent the outside faces of said carrier wheels inconcentric, parallel relation thereto and providing supports for theends of carriers located within said slots, a driving wheel havingdriving members thereon which engage the radial slots in said carrierrings causing said carrier wheel to roll said carriers along saidstationary tracks, a hopper mounted above said carrier wheel to storesaid carriers, a feed wheel having radial slots formed in the peripherythereof and mounted between said hopper and said carrier wheel, saidfeed wheel serving to transfer said carriers in succession from saidhopper to the radial slots in said carrier rings, an unloading rampdisposed between said carrier rings at a discharge station spaced fromsaid feed wheel, a delivery wheel at said discharge station havingradial slots formed in the periphery thereof to receive said carriersunloaded by said ramp, sensing means embodied in said unloading ramp forsensing a condition of the unloaded carriers, and means controlled bysaid sensing means for controlling the speed of rotation of said carrierwheel.

References Cited in the file of this patent UNITED STATES PATENTS1,382,149 Walker June 21, 1921 2,123,227 Bieling July 12, 1938 2,339,008Gladfelter et al. June 11, 1944 2,445,310 ChiloWsky July 20, 19482,516,908 Pottle Aug. 1, 1950 2,586,752 Weber et al. Feb. 19, 1952

